Promoter polymorphism G-6A, which modulates angiotensinogen gene expression, is associated with non-familial sick sinus syndrome

Matrix metalloproteinase 1 1 G/2 G gene polymorphism is associated with acquired atrioventricular block via linking a higher serum protein level

Limited studies are available regarding the pathophysiological mechanism of acquired atrioventricular block (AVB). Matrix metalloproteinases (MMPs) and angiotensin-converting enzyme (ACE) have been implicated in the pathogenesis of arrhythmia. However, the relationship between these molecules and acquired AVB is still unclear. One hundred and two patients with documented acquired AVB and 100 controls were studied. Gene polymorphisms of the MMP1 and ACE encoding genes were screened by the gene sequencing method or polymerase chain reaction-fragment length polymorphism assay, followed by an association study. The frequencies of the MMP1 −1607 2G2G genotype and MMP1 −1607 2 G allele were significantly higher in the AVB group than that in the controls (OR = 1.933, P = 0.027 and OR = 1.684, P = 0.012, respectively). Consistently, the level of serum MMP1 was significantly greater in acquired AVB patients than that in controls (6568.9 ± 5748.6 pg/ml vs. 4730.5 ± 3377.1 pg/ml, P = 0.019). In addition, the MMP1 2G2G genotype showed a higher MMP-1 serum level than the other genotypes (1G1G/1G2G) (7048.1 ± 5683.0 pg/ml vs. 5072.4 ± 4267.6 pg/ml, P = 0.042). MMP1 1 G/2 G gene polymorphism may contribute to determining the disease susceptibility of acquired AVB by linking the MMP serum protein level.

Conditional Up-Regulation of SERCA2a Exacerbates RyR2-Dependent Ventricular and Atrial Arrhythmias

Ryanodine receptor 2 (RyR2) and SERCA2a are two major players in myocyte calcium (Ca) cycling that are modulated physiologically, affected by disease and thus considered to be potential targets for cardiac disease therapy. However, how RyR2 and SERCA2a influence each others’ activities, as well as the primary and secondary consequences of their combined manipulations remain controversial. In this study, we examined the effect of acute upregulation of SERCA2a on arrhythmogenesis by conditionally overexpressing SERCA2a in a mouse model featuring hyperactive RyR2s due to ablation of calsequestrin 2 (CASQ2). CASQ2 knock-out (KO) mice were crossbred with doxycycline (DOX)-inducible SERCA2a transgenic mice to generate KO-TG mice. In-vivo ECG studies have shown that induction of SERCA2a (DOX+) overexpression markedly exacerbated both ventricular and atrial arrhythmias in vivo, compared with uninduced KO-TG mice (DOX-). Consistent with that, confocal microscopy in both atrial and ventricular myocytes demonstrated that conditional upregulation of SERCA2a enhanced the rate of occurrence of diastolic Ca release events. Additionally, deep RNA sequencing identified 17 downregulated genes and 5 upregulated genes in DOX+ mice, among which Ppp1r13l, Clcn1, and Agt have previously been linked to arrhythmias. Our results suggest that conditional upregulation of SERCA2a exacerbates hyperactive RyR2-mediated arrhythmias by further elevating diastolic Ca release.

Transforming Growth Factor-β1 T869C Gene Polymorphism Is Associated with Acquired Sick Sinus Syndrome via Linking a Higher Serum Protein Level

Background

Familial sick sinus syndrome is associated with gene mutations and dysfunction of ion channels. In contrast, degenerative fibrosis of the sinus node tissue plays an important role in the pathogenesis of acquired sick sinus syndrome. There is a close relationship between transforming growth factor-β1 mediated cardiac fibrosis and acquired arrhythmia. It is of interest to examine whether transforming growth factor-β1 is involved in the pathogenesis of acquired sick sinus syndrome.

Methods

Overall, 110 patients with acquired SSS and 137 age/gender-matched controls were screened for transforming growth factor-β1 and cardiac sodium channel gene polymorphisms using gene sequencing or restriction fragment length polymorphism methods. An enzyme-linked immunosorbent assay was used to determine the serum level of transforming growth factor-β1.

Results

Two transforming growth factor-β1 gene polymorphisms (C-509T and T+869C) and one cardiac sodium channel gene polymorphism (H588R) have been identified. The C-dominant CC/CT genotype frequency of T869C was significantly higher in acquired sick sinus syndrome patients than in controls (OR 2.09, 95% CI 1.16–3.75, P = 0.01). Consistently, the level of serum transforming growth factor-β1 was also significantly greater in acquired sick sinus syndrome group than in controls (5.3±3.4 ng/ml vs. 3.7±2.4 ng/ml, P = 0.01). In addition, the CC/CT genotypes showed a higher transforming growth factor-β1 serum level than the TT genotype (4.25 ± 2.50 ng/ml vs. 2.71± 1.76 ng/ml, P = 0.028) in controls.

Conclusion

Transforming growth factor-β1 T869C polymorphism, correlated with high serum transforming growth factor-β1 levels, is associated with susceptibility to acquired sick sinus syndrome.

Association of the angiotensinogen M235T polymorphism with recurrence after catheter ablation of acquired atrial fibrillation

PURPOSE

Previous studies showed that genetic variants of the angiotensinogen (AGT) gene conferred higher risk for acquired atrial fibrillation (AF). The present study investigated whether AGT variants correlate with the clinical outcome in patients with acquired AF after catheter ablation (CA).

METHODS

A total of 150 acquired symptomatic drug-refractory AF patients (mean age 63.7±11.0 years, 24.6% non-paroxysmal AF) with acquired AF underwent a single CA procedure in our department and were included in this retrospective analysis. Eight tagging single nucleotide polymorphisms (tSNPs) in the AGT gene were genotyped. Standard electrocardiographs (ECGs) and 24-hour Holter recordings were performed during a median follow-up period of 57.5 months to detect AF recurrence.

RESULTS

Sixty-one patients (40.7%) suffered AF recurrences after a single CA procedure during follow up. Of the eight tSNPs, the frequency of the M allele of M235T was significantly higher in the recurrence group (28%) compared to the non-recurrence group (18%) (p=0.042). The recurrence rates of patients with the TT, MT, and MM genotypes were 34.4%, 50%, and 55.6%, respectively (ptrend=0.049). After adjusting for age, sex, body mass index, hypertension, left atrial volume index (LAVI) and other covariates, M235T increased the risk of AF recurrence in additive and dominant models with odds ratios of 2.023 (95% confidence interval (CI): 1.034-3.926, p=0.033) and 2.601 (95% CI: 1.102-6.056, p=0.025), respectively. However, in multiple correction analyses, the p values of multiple comparisons were not statistically significant (pcorrect>0.05).

CONCLUSIONS

The M allele of M235T might be associated with an increased risk of AF recurrence after CA. Genotyping may thus be helpful on identifying patients with higher risks of AF recurrence after CA and developing optimal follow-up strategies. These strategies may differ and should be individualized according to patients' genotype. Future studies are warranted to validate the potential effect of AGT M235T on AF recurrence post CA.

Sick sinus syndrome and atrial fibrillation in older persons - A view from the sinoatrial nodal myocyte

Sick sinus syndrome remains a highly relevant clinical entity, being responsible for the implantation of the majority of electronic pacemakers worldwide. It is an infinitely more complex disease than it was believed when first described in the mid part of the 20th century. It not only involves the innate leading pacemaker region of the heart, the sinoatrial node, but also the atrial myocardium, predisposing to atrial tachydysrhythmias. It remains controversial as to whether the dysfunction of the sinoatrial node directly causes the dysfunction of the atrial myocardium, or vice versa, or indeed whether these two aspects of the condition arise through some related underlying pathological mechanism, such as extracellular matrix remodeling, i.e., fibrosis. This review aims to shed new light on the myriad possible contributing factors in the development of sick sinus syndrome, with a particular focus on the sinoatrial nodal myocyte. This article is part of a Special Issue entitled CV Aging.

Identifying potential functional impact of mutations and polymorphisms: linking heart failure, increased risk of arrhythmias and sudden cardiac death

Researchers and clinicians have discovered several important concepts regarding the mechanisms responsible for increased risk of arrhythmias, heart failure, and sudden cardiac death. One major step in defining the molecular basis of normal and abnormal cardiac electrical behavior has been the identification of single mutations that greatly increase the risk for arrhythmias and sudden cardiac death by changing channel-gating characteristics. Indeed, mutations in several genes encoding ion channels, such as SCN5A, which encodes the major cardiac Na⁺ channel, have emerged as the basis for a variety of inherited cardiac arrhythmias such as long QT syndrome, Brugada syndrome, progressive cardiac conduction disorder, sinus node dysfunction, or sudden infant death syndrome. In addition, genes encoding ion channel accessory proteins, like anchoring or chaperone proteins, which modify the expression, the regulation of endocytosis, and the degradation of ion channel a-subunits have also been reported as susceptibility genes for arrhythmic syndromes. The regulation of ion channel protein expression also depends on a fine-tuned balance among different other mechanisms, such as gene transcription, RNA processing, post-transcriptional control of gene expression by miRNA, protein synthesis, assembly and post-translational modification and trafficking. The aim of this review is to inventory, through the description of few representative examples, the role of these different biogenic mechanisms in arrhythmogenesis, HF and SCD in order to help the researcher to identify all the processes that could lead to arrhythmias. Identification of novel targets for drug intervention should result from further understanding of these fundamental mechanisms.